Multiposition cylinders in general are well known. They find common use to control position of, e.g., conveyance system rails as may be used in bottling processing plants. Conventionally, such cylinders provide the ability to achieve a plurality of discrete positions (e.g., 0″, 0.5″, 1.0″, 1.5″ for a 4 position cylinder) only. Typically, prior art multiposition cylinders (as shown in FIG. 1) involve designs where two or more cylinders (“sub-cylinders”) are stacked on one another. The bottom or rear cylinder is typically shorter than the one stacked atop it. More generally, a rearward cylinder is shorter or at most the same length as a cylinder that is forward of it.
In the prior art three position cylinder of FIG. 1, position 1 (the no-control or rest position) is achieved with both pistons retracted towards the rear (right in this figure) of the positioner while position 2 is achieved with the rear piston extended. With regard to position 2, upon application of pressure behind the rear piston, the rear piston is moved to its maximal displacement relative to the rear end cap; the piston rod from the rear piston pushes the front piston forward by an equal amount, effectively moving the front piston—and the positioning rod extending therefrom—forward whatever distance the rear piston extended. Position 3 is achieved upon application of pressure behind the front cylinder (when the device is in position 2), thereby causing it to move to its maximal extended position, thereby further extending the positioning rod's position by an equal amount (note that the front piston is not attached to the piston rod that extends from the rear piston). The piston rod extending forward from the front piston passes through a seal in the top cylinder end cap; displacement of the front piston, whether primarily effected by the front piston (position 3, after earlier repositioning thereof is effected by the rear piston) or the rear piston (position 2), results in repositioning relative to the stationary front end cap of the positioning rod that extends out of the front of the device. It is of note that there is typically a vent in the left-most wall of the chamber that the left piston travels in.
Disadvantages of conventional multiposition cylinders may include:
Size: For each discrete position (other than that position associated with zero extension), a cylinder of length at least as great as the distance from the previous position (stroke) is required. Most conventional multiposition cylinders include two or more cylinders stacked one atop each other (see, e.g., FIG. 1); for each discrete position a cylinder of corresponding stroke is required.
Example: A conventional four position multiposition cylinder with 1″, 2″, and 4″ strokes would typically include 3 cylinders. The first would have a stroke of 1″, the second a stroke of 2″, the 3rd a stroke of 4″; the combined length of this 4 position cylinder would be 1″+2″+4″=7″, plus whatever the thickness of the end caps and pistons (e.g., 3″ inches on a typical conventional 2″ multiposition cylinder). So, upon adding the end cap thickness (for each cylinder) to the piston lengths, the overall length is (1+3)+(2+3)+(4+3)=16″ . . . quite large for a cylinder having a maximum effective stroke of only 4″. If “efficiency” shows the relationship between effective stroke length and overall cylinder length (efficiency=effective stroke/overall cylinder length), the cylinder efficiency of this conventional four position cylinder is a mere 25%, and the cylinder must be 4× the required stroke length. Due to space constraints efficiencies greater than 50% are desired. At least one embodiment of the inventive technology may achieve this goal.
Control Inputs: Conventionally available, “off-the-shelf” multiposition cylinders typically require one air input for each position. For the 4 position example given above, each cylinder has an inlet which needs a valve to engage it. Each inlet has its own valve: turn valve 1 on and pressure is supplied to the 1″ stroke cylinder; turn valve 2 on and pressure is supplied to the 2″ cylinder; turn valve 3 on and pressure is supplied to the 4″ cylinder. If the cylinder is not supporting a mass or spring loaded object (supplying a sufficient retraction force), either a 4th valve or regulated air must be supplied to the rod side of the last-to-extend piston (the 4″ cylinder in the above example) to retract the pistons and return to the desired discrete position (whether that be 3″, 1″ or 0″). Each input requires a valve, airline, and inlet/outlet if the system is electrically controlled via a panel (as is generally the case for industrial equipment). Of course, such an apparatus can be rather complex, having many parts and involving a rather complicated control scheme.
It is of note that certain embodiments of the inventive technology may have arisen from the need to achieve a greater stroke length than is offered by cylinders having relatively high spring constants (such cylinders incorporating such stronger springs in order to achieve higher resolution positional control). As is well known, the higher the spring constant, the less displacement that spring will show under a certain force, thereby allowing for a greater resolution and more precision positional control. However, use of such springs comes with a limited range of motion, as in order to achieve positional ranges associated with lighter springs (which offer lower resolution control), comparatively higher pressures must be used, and often such higher pressures are impractical, not feasible, or simply dysfunction given the design. Aspects of the inventive technology, which may involve “staging” motion of the positioner (such that incremental control of the second movable component can be achieved from different “base”, or distinct, staged, positions of the first cylinder (at which the first movable component may be secure)), may resolve such concerns.